Filter/separators have been used in the aviation fueling industry for decades. These devices generally contain filter cartridges which also act either as a coalescer or separator. The separators of the prior art typically comprise a fluoropolymer coated onto a metal screen which has been formed into a cylinder. The fluorocarbon coating imparts water repellency to the filter, thereby causing the water to separate from the filtered stream. However, the process for applying the coating, as well as the fluoropolymer coating itself, continue to be relatively expensive.
In an effort to improve separators, while at the same time making them more cost effective, other screen materials have been utilized in the recent prior art devices. Specifically, screens made from plastic materials have been favored. Plastic screens may be formed with more threads per square inch than metal screens, due to smaller filament diameters and more efficient manufacturing methods. Moreover, alternative hydrophobic coatings applied to plastic screens are generally silicone-based compounds which are less expensive than fluoropolymers.
Plastic screens used in the conventional separators are extremely flexible. Accordingly, the plastic screens must be adequately supported within the separator to perform the filtration and water separation to resist collapsing due to operational pressures of the fluid passing therethrough. Preferably, the screen must be maintained in a smooth taut cylindrical configuration. Satisfactory results have typically been achieved by placing the screen material over a metal tube perforated to create 55 to 60 percent open area. A practical limit for circular apertures is 62% open area. It has been found to be difficult to form a metal support tube having a greater amount of perforated area, which also returns the rigidity necessary to support the surrounding plastic screen under the typical operating conditions.
It would be desirable to produce a separator cartridge wherein the support tube for the screen may be provided with greater open area.